For treatment of asthma, there has been hitherto applied multiple treatments such as treatment with drugs, treatment by change of air, treatment by desensitization, psychological treatment, etc., but there has not yet been established a method to accomplish a satisfactory therapeutic effect.
The drugs which have been nowadays utilized conventionally as an antiasthmatic drug include a .beta.-receptor-stimulating agent, a xanthine agent, a steroidal agent, an antihistaminic agent, an inhibitor of chemical mediator and the like. However, it is the present status that such various antiasthmatic agents have both merits and demerits, respectively, and all of them could not accomplish a satisfactory therapeutic effect.
Pathophysiology of asthma has not yet been completely elucidated and it is believed that its occurrence would arise from final reflection from complex pathologic conditions. Thus, the drug which could show multiple pharmacological actions rather than a sole action would be preferable as an antiasthmatic drug.
Recently, it has been elucidated and given attention that SRS-A, i.e. Slow Reacting Substance of Anaphylaxis, which has been known for a long time to be one of important chemical mediators for immediate anaphylaxis or asthma, is a metabolite of arachidonic acid by 5-lipoxygenase pathway, that is a mixture of luekotrienes C.sub.4, D.sub.4 and E.sub.4. Leukotrienes are considered to be a potent chemical mediator for allergic or inflammatory reactions and cause such disorders as contracts of smooth muscles, e.g. bronchial muscle or pulmonary blood vessels, or increased vascular permeability and the like. Further, it has been elucidated that they could show such actions as promotion of mucosus secretion, decrease in ciliary movement, contraction of coronary blood vessel and so on.
Moreover, it has been suggested that histamines, leukotriene B.sub.4, PAF of prostaglandins, e.g. PGF.sub.2x, PGD.sub.2, TXA.sub.2, in addition to SRS-A, could participate in allergy or inflammation.